Femoral forces during limb lengthening in children

A system was designed to measure forces during femoral lengthening using force transducers on an Ilizarov femoral frame. Measurements were made in three teenaged subjects overnight and during weight bearing. A progressive increase in axial load secondary to distraction was seen, forces peaking at 428, 447, and 673 N for the three subjects. Little change in force transmitted by the frame was observed during weight bearing. Measurements taken before and after each individual lengthening showed no change in axial force or bending moment (p > 0.01). A diurnal variation of axial load was found (p < 0.01). Forces at midnight were greater than in the morning in all the subjects, with a mean difference of 113 N (p < 0.01). Distraction forces measured in the femur during distraction are greater than those previously measured in the tibia. Evidence exists that the callus is stiff and may be the origin of these forces.